RFR: 7877: Update the jmc version in jmc8 branch to 8.2.1

[Marcus Hirt]

Unless there is any other feedback before next Wednesday, I'll set the ga tag at the next JMC dev meeting.

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Commit messages:
 - Minor fixes
 - 7877: Update version to 8.2.1

Changes: https://git.openjdk.org/jmc/pull/421/files
 Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=421&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-7877
  Stats: 212 lines in 147 files changed: 0 ins; 0 del; 212 mod
  Patch: https://git.openjdk.org/jmc/pull/421.diff
  Fetch: git fetch https://git.openjdk.org/jmc pull/421/head:pull/421

PR: https://git.openjdk.org/jmc/pull/421